Chronology and stratigraphy of the Magdalen Islands archipelago from the last glaciation to the early Holocene: new insights into the glacial and sea‐level history of eastern Canada

Abstract

The Magdalen Islands (Québec, Canada) are a key location for unravelling the glacial and sea‐level history of the Maritime Provinces of eastern Canada. Although many sedimentary sequences have been described in the literature, absolute ages are lacking, impeding an accurate interpretation of the deposits and the establishment of a precise chronological framework. This study provides a detailed description of 21 stratigraphical sequences located throughout the archipelago, as well as the first comprehensive luminescence chronology from the Last Glacial Maximum (LGM) to c. 10 ka. In addition to the five samples collected for age control purposes, 34 luminescence samples were taken from 17 different sites in glacial, periglacial and coastal deposits. The stratigraphical and chronological data reveal that the islands were at the crossroads of two icecaps during the LGM; the southern islands were glaciated by the Escuminac icecap located in the western Gulf of St. Lawrence whereas the northern archipelago was glaciated at the end of the LGM by an ice flow from Newfoundland. The glacial deposit covering the northern Magdalen Islands was associated with the Newfoundland icecap; here it is named the Grande‐Entrée till and is dated to c. 20 ka. OSL ages between c. 23 and 17 ka acquired from cryopediment and coastal deposits on the southern islands indicate that this part of the archipelago was deglaciated shortly after the LGM and was affected by a high sea level and periglacial processes. Around 15 ka, the entire archipelago was deglaciated and partially submerged until c. 10 ka. This data set is the first major contribution to a detailed chronology of the Magdalen Islands and constitutes the first step towards interpreting the glacial and sea‐level history of the central area of the Gulf of St. Lawrence; this new understanding will provide input to regional marine and glacial modelling.